The present invention relates to an indicator of a variable for an aircraft.
More particularly, although not exclusively, it relates to an indicator of altitude and of vertical speed (which is the derivative with respect to time of the variable representing the altitude) for an aircraft.
It is known that for an aircraft, for example a helicopter or an airplane, when climbing (or descending), the acquisition of a given altitude, for example a flight level imposed by air control, is generally performed at a stable vertical speed.
On the approach to the intended altitude, the pilot of the aircraft progressively reduces its vertical speed so as to intercept said altitude with a vertical speed low enough to avoid any significant overshoot of the intended altitude.
This reduction in the vertical speed on approaching the intended altitude can be performed by intuition or with the help of empirical rules by monitoring the alterations (in position and in speed) of the altitude indication [needle for conventional instrumentation or index on symbology known in aeronautics by the acronym EFIS (Electronic Flight Instruments System)].
For example, a common empirical rule consists in commencing the reduction in the vertical speed on overstepping a fraction of the deviation between the intended altitude and the current altitude ({fraction (1/10)} for example), then in repeating this approach so as to progressively reduce the vertical speed.
Nevertheless, whatever strategy is used (intuition or with the help of an empirical rule), these methods require, on the one hand, good knowledge and good conduct of the performance of the aircraft and give rise, on the other hand, to a considerable work load in a phase of change of flight circumstance, that is to say when the pilot must devote himself to other tasks relating, for example, to air traffic or to navigation. Consequently, none of these known methods is satisfactory, the difficulties of organization and of gaging being due essentially to the fact that the standard instruments are not organized so as to depict an obvious summary of the situation.
To try to afford a solution to this problem, the documents EP-0 324 195 and FR-2 742 226 each disclose an altitude and vertical speed indicator making it possible to remedy, at least partially, the aforesaid drawbacks. To this end, the indicator disclosed by the document FR-2 742 226 comprises:
first and second sensors of altitude and vertical speed of the aircraft, respectively;
means for processing the signals delivered by said first and second sensors; and
means for displaying the processed signals depicting on a display screen:
altitude indication means, and
vertical speed indication means arranged opposite said altitude indication means,
said altitude indication means and said vertical speed indication means being coupled so that the altitude indication situated opposite the vertical speed indication represents, at any instant, a forthcoming altitude for the current vertical speed.
Thus, once the vertical speed indication arrives opposite the intended altitude indication, it is sufficient to keep the vertical speed indication locked onto the intended altitude indication until the latter is attained, this resulting in a progressive reduction in the vertical speed until an at least substantially zero vertical speed is reached. This known indicator consequently makes it possible to provide the pilot of the aircraft with an analog and coupled altitude and vertical speed indication, on a display screen, making it possible to guide any barometric (or radar) altitude capture without displaying the current value of the altitude of the aircraft, except when the intended altitude has actually been reached.
Moreover, in this known document FR-2 742 226, said altitude indication means consist of a graduated scale, rectilinearly (vertically) mobile past a fixed mark, and said vertical speed indication means consist of a needle mobile in rotation about the point of intersection of the extension of said fixed mark and of the extension of said needle and pointing toward said mobile scale, the angle defined by said fixed mark and said needle being representative of the value of the vertical speed.
Consequently, this known indicator enables the pilot of the aircraft to easily modulate the vertical speed so as to accurately capture and follow a desired altitude. At the moment of capture, the aircraft therefore exhibits a zero or substantially zero vertical speed.
Such a mode of interception, which is particularly advantageous for meeting up with a specified altitude or for capturing a trajectory with zero slope, cannot be applied to the interception of a trajectory exhibiting a nonzero slope since, with this known mode of interception, the aircraft captures the trajectory with a zero vertical speed, while this vertical speed ought to be such that it makes it possible to follow the trajectory (with nonzero slope) as soon as it is intercepted.
Also, to intercept a slopewise target trajectory, for example an approach trajectory, the pilot of the aircraft generally performs the following operations:
he determines beforehand by calculation the vertical speed factor making it possible to follow the slope while taking account of the ground speed of the aircraft;
he displays a vertical interception speed making it possible to converge toward the slopewise trajectory; and
on the approach to the slopewise trajectory, he progressively modulates the vertical speed, on the one hand so as to intercept said trajectory without significant overshoot and, on the other hand, so as to alter his vertical speed from the interception value to the value for following (also determined beforehand by calculation).
Once the interception has been achieved, the same strategy is applied each time the aircraft exhibits a significant deviation with respect to the target trajectory.
This known method of intercepting a slopewise target trajectory thus exhibits the same drawbacks as those stated above relating to the known methods of approach, by intuition or with the help of empirical rules, to a specified altitude. In particular, it requires, on the one hand, good knowledge and good conduct of the performance of the aircraft and gives rise, on the other hand, to a considerable work load in a particular phase of flight, in which the pilot generally has to devote himself to other tasks relating, for example to air traffic or to navigation. This known method of intercepting a target trajectory exhibiting a nonzero slope is therefore scarcely satisfactory.
The object of the present invention is to remedy these drawbacks. It relates to an indicator of a variable for an aircraft, providing a pilot of the aircraft with a visual guide which is integrated into an environment which is familiar to him and which enables him to anticipate and to gage in an optimal manner the piloting of the aircraft so as to capture and follow a target trajectory.
To this end, the indicator of a variable and its derivative for an aircraft, comprising:
first means for determining the variable and its derivative with respect to time; and
display means which depict on a display screen:
to indicate said variable, a graduated scale which bears values relating to said variable and which is rectilinearly mobile past a fixed mark, marking the value of said variable of said aircraft; and
to indicate said derivative, an indicator element,
is noteworthy in that it furthermore comprises second means for determining a first target value relating to said variable and a second target value relating to said derivative, and wherein said display means furthermore depict on said display screen:
a first means of indication of the first target value, which is arranged in such a way as to indicate said first target value on said graduated scale; and
a second means of indication of the second target value, which is associated at least with said indicator element so that, when the latter points toward said second means of indication, said variable of the aircraft approaches said first target value until it is substantially equal to the latter and as appropriate remains substantially equal to said first target value, while said derivative is substantially equal to said second target value.
Thus, by virtue of the invention, to implement the desired piloting, that is to say to contrive matters so that said variable becomes substantially equal to and remains equal to its target value (first target value), it suffices for the pilot simply to control the aircraft in such a way as to keep said indicator element (derivative of the variable) pointed at said second means of indication (target value of said derivative).
Consequently, a variable is controlled by way of its derivative with respect to time.
It will be noted that the present invention is applicable for example to a horizontal plane or a vertical plane, or even to any plane.
In a first embodiment (relating to piloting in a vertical plane), said indicator is an indicator of altitude (variable) and of vertical speed (derivative).
In this case, said altitude and vertical speed indicator is noteworthy, according to the invention, in that it includes:
said first means for determining the altitude and the vertical speed of the aircraft;
said display means, which depict on the display screen:
to indicate the altitude, the graduated scale which bears altitude values and which is rectilinearly mobile past the fixed mark, marking the value of the altitude of said aircraft; and
to indicate the vertical speed, said indicator element comprising a needle which is mobile in rotation about the point of intersection of the extension of said fixed mark and of the extension of said needle and which points toward said graduated scale, the angle defined by said fixed mark and said mobile needle being representative of the vertical speed of said aircraft; and
said second means for determining a target altitude and a target vertical speed which correspond, respectively, to the altitude of a target trajectory and to the vertical speed making it possible to capture and as appropriate to follow said target trajectory, and wherein said display means furthermore depict on said display screen:
said first means of indication of the target altitude, which is arranged in such a way as to indicate said target altitude on said graduated scale bearing altitude values; and
said second means of indication of the target vertical speed, which is associated at least with said mobile needle so that, when the latter points toward said second means of indication, said aircraft meets up with and as appropriate follows said target trajectory at said target vertical speed.
Thus, by virtue of the invention:
in order to achieve the capture of the target trajectory, it is sufficient for the pilot simply to command the aircraft in such a way as to keep said needle pointed at said second means of indication;
the altitude deviation between the actual altitude of the aircraft and the corresponding altitude of the target trajectory is displayed clearly and accurately by the relative positioning or the deviation between said fixed mark (indicating the actual altitude of the aircraft) and said first means of indication (indicating the target altitude);
the capture of the target trajectory is therefore displayed by the facing positioning (zero altitude deviation) of said fixed mark and of said first means of indication; and
after capture, in order to achieve the following of the target trajectory, it is sufficient for the pilot to simply command the aircraft in such a way as to keep said needle pointed at said second means of indication.
Consequently, the indicator in accordance with the invention provides a pilot with a visual guide enabling him to pilot the aircraft optimally so as to capture and follow any target trajectory (with zero or nonzero slope).
Moreover, the elements envisaged in accordance with the invention are arranged on a known indicator, that is to say are integrated into an environment which is familiar to the pilot, thereby facilitating the understanding and the reading of the various information displayed.
Furthermore, advantageously:
said first means of indication comprises a mark which is mobile and which is provided on said graduated scale; and
said display means moreover depict on said display screen a reading window, revealing a part of said graduated scale, and said first means of indication is formed in such a way as to display the numerical value of said target altitude, when said mobile mark arrives at one of the ends of said reading window.
Additionally, according to the invention, said second means of indication is symbolized on said display screen by a first straight line segment which is inclinable, the inclination of said first straight line segment being representative of the vertical speed making it possible to follow the target trajectory, and which is arranged in such a way that its direction coincides with the direction of said needle when the aircraft is situated on the target trajectory and is following it.
Moreover:
in a first embodiment, said first straight line segment is arranged on said graduated scale, so that said straight line segment and said needle are aligned at the time of capture and during the following of the target trajectory; and
in a second embodiment, said first straight line segment is arranged on a vertical speed scale defined at the level of said needle, so that said straight line segment and said needle are in this case superimposed at the time of capture and during the following of the target trajectory.
Additionally, in particular to facilitate the reading of said indicator, advantageously, said display means furthermore depict on said display screen a second straight line segment joining said mobile mark (indicating the target altitude) to said first straight line segment (indicating the vertical speed making it possible to follow the target trajectory).
Furthermore, advantageously, said second means determine a target trajectory exhibiting at least two successive rectilinear portions, of different slopes, and said display means moreover depict on said display screen a visual symbol alerting a pilot of the aircraft to a future change of the current portion, to which said aircraft is guided, thereby making it possible to alert the pilot to a change of flight configuration.
Moreover, advantageously, said visual symbol, preferably a flashing disk, is arranged in such a way as to indicate the vertical speed making it possible to follow the portion of the target trajectory, which follows said change of current portion.
Furthermore, according to the invention, when said aircraft is furnished with an automatic pilot, advantageously, said automatic pilot is formed in such a way as to receive and to use the information relating to the target vertical speed so as to meet up with and follow said target trajectory automatically.
Additionally, in a second embodiment (relating to piloting in a horizontal plane, that is to say a plane exhibiting a substantially constant altitude), said variable corresponds to the speed of the aircraft, said derivative to its acceleration, said first target value to a target speed and said second target value to a target acceleration, all these parameters being defined in said horizontal plane exhibiting a substantially constant altitude.
In this case, said indicator element can comprise:
a needle which is mobile in rotation about the point of intersection of the extension of said fixed mark and of the extension of said needle and which points toward said graduated scale, the angle defined by said fixed mark and said mobile needle being representative of the acceleration of said aircraft in said horizontal plane; or
simply an arrow indicating the acceleration.
The elements of said first embodiment, described above, can moreover be integrated by analogy, into this second embodiment.